The purpose of the CASP experiments and workshops is to provide independent assessment of macromolecular structure modeling methods. With the success of genome-wide sequencing, determination of the corresponding DNA-encoded structures becomes increasingly important. Extensive knowledge of protein structures will significantly aid the investigation of macromolecular function, interactions, and biochemical pathways. It will also have a major impact on the understanding of biology and human disease, and eventually on drug design. In spite of substantial progress, experimental determination of structure remains inherently time-consuming and costly, and has provided coverage of less than 1% of the known sequences. Computational modeling techniques provide coverage of a much higher fraction of sequences, albeit at lower accuracy. The primary goals of CASP are to establish the capabilities and limitations of current methods of modeling structure from sequence, to determine where progress is being made, and where the field is held back by specific bottlenecks. Methods are assessed on the basis of the analysis of a large number of blind predictions of protein structure. These goals are achieved through a series of large-scale community experiments, conducted every two years, and accompanying workshops. The experiments involve well over 100 research groups from more than 20 countries. In each experiment, two preliminary workshops are concerned with planning and monitoring the experiment. The main workshop brings together the community of participating scientists for an intensive discussion and analysis of the results of the experiment. An additional goal of these workshops is to provide an opportunity to junior scholars and newcomers to the field to familiarize themselves with the most pertinent and most current issues in this area of science. The CASP workshops are not a typical conference but a culmination of the community experiment. Support is requested for the workshop component of the 11th, 12th and 13th CASP experiments.